Legacy display systems operate at a constant refresh rate in which a display image is updated at a fixed number of cycles per second. This fixed display refresh rate can create playback issues when displaying certain content. For example, a display panel having a 60 Hz refresh rate exhibit frame judder when viewing a 24 Hz movie, as the panel refreshes every 16.6 ms, whereas the frame is generated using 41.6 ms sample times, which is an uneven (e.g., 2.5) multiple of the frame duration. Accordingly, some frames are scanned by the display twice while others are scanned three times.
While some legacy displays allow the panel refresh rate to be reduced to a fixed refresh rate, visual quality may suffer. For example, blur may be introduced into animated or moving content when the display refresh rate is too low for the displayed content. Moving high spatial frequency images across the panel, such as text displayed while scrolling a web page or text document may appear blurry when refreshed at a low rate. In general, the higher the refresh rate of a display device, the sharper displayed animation becomes. Thus, a moving image displayed on a display having a refresh rate of 120 Hz may yield a visibly sharper image and may allow the text on the scrolling image to be legible under circumstances where such text would be blurred and illegible at lower refresh rates.
Additionally, higher refresh displays provide benefits other than temporal visual quality. For example, for touch input displays, the latency between a touch input and displaying a result of the touch input may ultimately be gated by how quickly a new, updated frame can be presented on the display. For example, if a display refreshes at 60 Hz, then a new frame generated based on a touch input may have to wait until the beginning of the next 16 ms period. Provided that a new frame is ready for display, an 120 Hz display reduces the response time by half of that of a 60 Hz display.
However, in most devices, particularly mobile and handheld devices, the display hardware consumes a tremendous amount of the overall energy budget of the device. Increasing the refresh rate may further increase the already large energy demands of operating the display. For example, in some displays, operating the display at 120 Hz instead of the standard 60 Hz generally supported by displays may result in up to a 150% increase in display power requirements. Thus, for a mobile device, a high display refresh can have a significant negative impact on battery-based operating time.